Tube tester



July 18, 1933. D, SPARKS 1,918,495

TUBE TE S TER Filed June 6, 1930 3 Sheets-Sheet 1 FIG 2 {2 o o n nnnnzl 2' I z I FIC74 IN V EN T 0R. b'

ATTORNEYS.

July 18, 1933. D E, SPARKS 1,918,495

TUBE TESTER Filed June 6, 1930 3 Sheets-Sheet 2 FIG 6 26 R so; 29 /22 *2 Sgwroza.

MKM W4 A TTORNEYS.

Patented July 18;

levee-mien v' This inventionrel'ates to tubetesters, and-L it has among its objects the provisionof imance plate impedance'lnd amplificiition factor, areidetermined by apply ng an alternating current potential from the normally available commercial alternating; current -f source to the'plate circuits of the tubes" while applyingflt'o the controhgrid a potent-ial de-' rived y from a rectifi d I alternating current flow from'said source I Q g "The foregoing and'other objects ofthein vention will be best understood from thefol lowing description of exemplifications there-i of, reference being drawingswhere'in I Figs. 1 to are diagrammatic views of tube testing arrangementsembodying my invent tron. v r c With th enormously increased use 0i radio had'to the accompat'ny ng tubes and the continuously multiplying sales, thereoflthere has been for'sometime past'a' very urgent demand for a reliable tube tester by means of which thequalities of the tubescould be determined by the salesrnzur at the time the tube is purchased, ThestOresandi in general, the placeswhere tubes are bought; are asa rulesupplied with ordinaryelternetk "'ing current end there has'beenteigi'sting, as

a result, especial demand for a tube tester that would be operated from. a regular-e14 ternating' current tap on the domestic line circuit, andyet enable the'dealer'as Well as the layman purchaser to see ate glance Whether the tubes purchased have the char:

acteristics required for satisfactoryoperav, y I e H inga verylstrong demandffor an' l'nstrurnent y and a method'flof tubetesting using'gordinary alternating currentfwhereby'the inutuetlco'n-j, d'uctancerating and other important chair? acteristics of'thetu'bes would be-obtzti'ned'by,

tion in the sets for which they are bought.

#Vith aview toi. supplying such demand,

there have been developed in the past two types T of alternatingficurrent operated tube tester's. 'One type isknownas the emission tester and is arranged so that the; fullfalter hating current platepotentialis applied to,

the grid and pl'ate'in parallel, 'and'the total emission of the 'filamentis measured with e used as a, of the tube; The limitations lo fythi's t-ypeof. f testingfepparaitlis aremanifoldi, tFirst ttlie i testing procedure-is rather involvedj "It' is f l ,firstnecess'agry to know theplatecurrent withf,v

one potential; applied it heugrid,"fthen i'toi know theplatef-current with another-poten tial'gap'plied were grim-rand third, td' isubtmct one reading"of xthe plate currentYfroni-thef otherianddete'rmine thechinge ofithepleite current. Thus thefprocedure requiresthree '8 y the plate current, third involving tcurrentindiczttinginstrument connected' in theplate circuit. -"Because of thela ck of correlation" between the total emission and: the

true merit of-the tube,"this test iscf little value in d-eterminingthe usefulness of tubes fora particular service, and this-type of tester has fo'und very little use, i i The other type of tester, whic-h I V has found Wide utilization, isthefse-called' grid-swing I tester, such as described in my co-pending; r

application Serial No. 236,044,filed*NoVemberl x 1 28th,11927., In this type, of instrument, the i H plate "circuit was energized from [an alternating jcurrent source an'd at the same time; different alternating current -;v0ltages were applied' tofthegrid, and theresulting varia' tions of the -fplete current measured; Y'lhe changesofthe platecurrentso'producedwere 1 measure of'the mutualjcondufctzince operations; tvv'o consis'ting of obselivdtions of mental calculation;

terms of thrhritriel conductinceg but rather in terms'ofthefchangelin plate'ciirrent. 1Wi th the greatly:increasediiumber of tubetypes, the testing ofthe tubelqualitiesby the de-w termiiiationofthe chztnge inthe plate vdltdge in the manner described aboveprovedinddefl r es cend limitation lies fii n th'eifaet thet he mer ts of the tube are determined not-in p quete, endes a result,;there"has beeneizist I1 a single direct observ aticinTone; calibrated i scale;

rent source and at the same time applying their amplificationfactor and plate imped I ause may. beread oii directly on a scale of. the instrument.

to the grid a potential derived from a rectified alternating current flow from said source, arrangements may be obtained whereby the mutual conductance of grid-controlled tubes,

In-the exemplification of my invention shown in Fig. 1a tube 1 comprising a filamentary cathode 2, a control grid3 and a,

plate. 4:, that is to be tested, is arrangedto be v 3 mounted in a socket of the testing instrument, the terminals of the tube electrodes engaging respectively, the cathode socket terminals 5,

the grid socket terminal (Sand the plate socket terminal 7 of the socket; The tube and the testing circuits thereof are arranged to be energized from a transformerlO have a pnmary winding 11 that is energized with ordi-v nary alternatingcurrent from a house source through conductors 12 leading from aplug 13-that may be inserted in a wall socket of the familiar type. A secondary Winding 14 of the'transformer is connected to the socket terminals 5 and'serves to supply thecathode filament 2. The plate terminal-7 isconnected through'a conductor 15 to one of the supply conductors 12 of the transformer. The plate circuit is completed by a conductor 16 con 'nectedto the other supply conductor 12 of,

former winding 20 through rectifier 21, conduct-or 22, switch 23, a resistance 26, variable "tap contact 29, conductor-17, meter 18 and conductor 25,back to the winding 20. From this circuit a potential is applied totthe grid 3 ofthe tube by means ofthe conductor 2i leadingffrom switchl23to-the grid socket terminal 6.' p r Assumingthat the transformer 10 is energized from a house current source of 110 1 Volts alternating current and the several )v and (-1-) signs on the respective windings,-and with the switch 23 open, a current willflowin theiplatecircuit of the tube from plate atothe cathode 2and thence by way of I the meter 18 in the direct-ion of the arrow 1,,

thro ugh conductor'lfi to the otherterminal of the supply source. The meter 18 will then have, a certain deflection indicating a certain plate current flowingthrough the tube. The

current flowing through this platecircuit has the 'form ofrectified current impulses, cur- ,rentfiowing only during-the half cycle when "the plate l is positive, there being no plate current during the half of each cycle when the plate is negative. No current flows at the moment through transformer winding 20 and rectifier21,as the switch 23 is open. The grid 3 will accordingly be substantially at the po-' tentialnofthe cathode 2 by reason of its-edirect connection through the currentless resistor 26 to the cathode lead fromtransformer winding 14 to cathode socket terminal 5.

If the switch 23 is closed, an additional current-flow is established'from the transformer winding 20 byway of therectifier 21, switch '23, resistor 26, meter 18, and return wise in the form of rectified current ime pulses, the current flowing only during the conductor :25, this current flow being like:

half-of each cyclewhen the voltage induced in transformer 20 is in the conductive direc tion of the rectifier 21. This flow. or. current by way of theresistor 26 produces across said; resistor a Voltage drop which is applied through the conductor 24: to the grid 3. The. applied grid voltage produces a change in plate current change, produced by the voltage I s5 the plate current and it is the balance of this 7 applied to thegrid, against the current flow;

from the rectifier 2O effected bytheclosureof r the switch 23 that I utilizefor direct: deter mination of the mutualconductance of the .tube 1 that is tested.

1 In accordance with my nvention, I arrange the polarity or thetransformer winding20 and of the rectifier 21 inthe circuit thereof so that current pulses fiowacross the resistor 26, during the half cycles when the current pulses flow'inthe plate circuitof the 'tubeby way from the plate, to the cathode. The circuitarrangement as shown in the drawings is i made suchv that the directionfof flow of the rectified current from the transformerwinding 20 by way ofthe meter 18 isopposite to the direction of the currentchange produced by; the application of the potential drop across the resistor 26 to the grid 3, of the tube. Thus, for instance, with thepolarity of transformer winding 20 and rectifier 21 as indicated in the drawings, if the current from the transformer winding 20 through the resistor 26 upon the closure of switch 23 is d esig-v H nated asI ndth cl -th l t transformerwindings 11, 14; and 20 are poled J 7 a e lange m e p a 3 Our relativelyto each other as indicatedby. the

rentfiow produced bythe application of the voltagedrop across the resistor 26 is desig-y I duced by the closure of the switch so that closure of the switch 23 does not change the deflection of the meter 18 against the position indicated by the meter when the switch 23is open. In otherwords, for instance,

if the meter 18, witli. the switch. 23- open, indicates, say; 8 milliamperes, the

resistance'26 may be so adjustedso that on closure of the switch '23 the meter indication established through the resistorflti' bvnthe' closure of switchfl It canbe'shownthat under such conditlons the. mutualconduct ance of the tube is equalto" the conductance of the part of the resistor 26 included jnthe" circuit" of the ransformer windingeQO -or designating the included resistanceb ypRj and the mutual conductance of the tube G We;

In order to permit direct reading of the mutual con ductancehof the Qtubeon' the instru by the equation mer t; i provide a scale gOtcalibratedl so that theadjustin'en't' oft-he contact tap 29 on the resistor .26 gives on the scale dire-ct readings ofthe mutual condnctance'oi the tube. V a

- T theoryofoperationofthisi de'viceiiiay heexplainedasfollows: f

The mutual conductance of the t ube is wherein l isthe change 0t the plate current {produced by a change of theugriduvoltage equal to Making Y 1 v .a 1 1; or as explained above; Wehave I i Efi x'lirl l- Substituting We obtain 7 that ductance of the tube.

Thevalues of mutual conductance obtained isfa in'easure gof lthemutual con with an arrangement as shown in Fig. 1 are;

somewhat different from the values of mutual conductance as" obtained by thestandard dircct current 'method-s. This is dueto the fact that, as distinguished-from directcun rent methods, where a1 constantiD. G; plate, voltage and D. C. grid voltage's are applied to the tube electrodes, in the arrangement of my invention pulsating voltages are applied to" the electrodes of the-tube. Accordingly, the a mutual conductance measured by my ar rangement is thequotient of the average'platecurrent change over the" average gridpoten-' tial appliedto the tubefTThe differences in the results of the measurements obtained Withiny arrangement. as "againstordinary direct current methods are however unobje'c tiona'ble because ior every practical purpose, the mutual conductance reading obtained by a. my arrangement is just as-"good an indication the average mutualfconductance of the tubeobtained by my r arrangement is for: every practical purpose as runy a indication of the performance" characteristics important for the -operation of: theftube in ord-inary radio receiving sets as that obtained by direct current, methods.- In some respects, the mutual conductance value of the tube ob tained; by a means of arrangement gives a better evaluation of the operating charm: v teristics of the tube, since it indicates the average performanceiover a range ofoperatv d ing voltages" under which the 1 tube is likely tobe nse'd, Wh ereas the; ordinary direct ourrent methods indicate the performance only under a fixed setflof operatingconditions In, the example Shown in theFdratvings, I the transformer winding and the r ce; her 21 are so poledagainsttheprimarytrans 1 former winding 11 that when the s'witchl23 is; closed,la, positive potential appliedby the drop across the resistor/26 to the grid 3 ofthe'tubeL A's a -result, the application of i a a 1 such grid potential fgives1anincrease inrthe plate current of theltube,Whichcurrent in creasev is indicated by the direction of the fl The arrangement will also operate if the I polarity of-thetransf ormer wind-ingQO and I v of the rectifier 2 1 is reversed-sothatonblos: ingthe switch 23,"'theirectifiedjdirectcure -1"ent wi1lfiow, in the direction {rem mans- I former Winding 20Fthroughvconductor 25; a V meter 18,;xcon'duct'0r 17, res'istor 26, switch J 23fcondi1ctor 22',-rectifieri21, back tothe winding (20, the "current being in this case: in th'edirection opposite'to thearrow IiwThiSc it v current flow vvill producelanegative voltage 1 I, drop across theresistor26so thatthe p"0ten-' a a r tialxappliedf-to" the grid} will "be negative with'irespectttothe cathode 2, resulting-fin a decrease ofthe'plate currentcorrespondingin, to a direction of flow opposite to the arrow arrow'lg, in the drawings. 1 a

I -in the drawings: Accordingly,-with such change in the plate current nae to the applicationof the negativegridpotential will" {I again oppose each other linfithe meter 18 J and aslin theiinstance described above,,Wh-en' the con tact tap 29 is so adjusted that these W currents. are equal and opposite,and closure 1 of wth.eswitchi'23 has no'efi'ect on the defiec-- 5 tion ofthe meter,'theconductance of' t he'" U part of the resistojr,v 26 includedfin "thecir ductance-of the tube "1,

cuit will bea measure of themutual con- 1 a,

' 1 Forlthe'zproperoperatibnfof the deviceQit is absolutely lessentialnthat ind matter I Whichdi're'ctionthe current flows fin thegcir-., p

lcuit the 1 transformer inding 20 and the 3. a I

rectifier 21, the currentflow takes place duri'ng the halt-cycle when current flows y. from theplate to thecathodei For instance, if

p the circuit arrangement had thetransformer winding 21poled1as shown in Fig. 1, but the rectifier 21 connected with reverse polarity, the arrangement would fail to operatein the manner contemplated for producing an in- Y dication of the mutual conductance of the tube becauscthe currentin the circuit of'the transformer winding would flow during the half cycle when no 'current is flowing in i the plate circuit, so that the resulting applicationof a grid potentialtothegrid 3 would have no eil'ect' on the operation of the tube and the current I through the meter 18 would have nomeaning as far as a comparison with plate current conditions is concerned;v The' idea underlying my invention, namely the application to the gridof auxiliary voltagederived fromla flow of'rectified current from the alternating current source is not "limitedto arrangements for determining the 7 inutual conductance of the tube but'itis'likewise applicable toa variety'of other arrangements, for instance, for determining the amplification factor or the plate impedance of the tube. l 303 An arrangement for determining the amplification factor is shown diagrammatically I in Fig.2. A three-electrode tube 1 like the tube shownin Fig. 1 is arranged for mount 1 ing'in asocket having socket term1nals5, 6,

.353 and 7 The cathode. and plate are energized from a transformer .10 in a way similar to v the arrangement of Fig. 1,'a meter 18being included in the. return circuitof the plate and 'thefcathode. An auxiliary circuit is arranged to be supplied from a'transformer 'windi-ng 20 through a, rectifier 21 and the switch 23, the auxiliary circuit including two 'resistors26 and 27 The amount of resistance included in the plate circuit may be varied by means of a slidable contact member 29'on the resistor 27 "'When theswitch23is open and the tube 1 mounted inplace, with the transformer winding 11 energized from the alternating current line, a current will flow m theplate circuit. of the tube from plate 4: to cathode 2 by way of tliemeter' 18, producing a deflection of the meter. Onclosing of switch 23, an auxiliary rectified currentflow a will heproduced from transformer winding.

2Oby way of the resistance 26 and 27. sThe voltagedrop across resistor 26 is'applied" through the conductor-24: to the grid, producing a change in thcplate' current which may herebe designated as I thisqcurrent being in-dicated in the drawings bya correspondingly designated arrow. There is also produced a voltage drop across the-part of the resistor 27 leading to the contact tap 29, whichvoltagedrop is directly inthe plate circuit of tube and acts, with'the polarities of the elements "the plate impedance. I

- have v as indicated in the drawings,j subtractively'.

relatively to the plate voltage appliedby the connections of the plate circuit to the con ductors 12 ofthesupply source. Accordingly, the plate voltage will be reduced and give a decrease'of the plate potential. As a result, there will take place a change of the plate current produced by this decrease of plate potential, this change of the being designated as and belng shown in the 'drawings by a correspondingly marked arrow. f o

.' By adjusting the slidingtap 29 011 the resistor 27, the current flow conditions in the auxiliary circuit through the resistors 26 and 27 may be varied so that upon closure of the switch 23, the current change I produced in the plate circuit by the variation'of the grid potential will be balancedby the cur-.

rent I produced in the; plate circuit by'the variation of the plate potential, so that the closure of the switch'23 will not afiect the deflection of the instrument 18. Under such conditions, the part of theresistor included in the plate circuit'is a measure of the amplification factor ofthe tube, and a scale 30 suitably calibratedin accordance with theresistance27 will give a direct indication late current I of the amplification factor. Thetheory of,

this arrangementmay be explained as follows: i Q o The increasein the late current due to the application'of the grld potential 13);, to the 7 grid is given by the equation? I 6 R, I

where u is the amplification factor and R is The change in the plate current produced by the change in the plate voltage due to the drop across the resistor 27 is given by equa- F .where R'designates theresistance ofthe part of resistor 27 included inthe plate circuit, andR the resistance of the resistor-26, we

drzj (1a).

As in connection with the arrangement 'with a direct-current instrument on account 7 of theff act that the "average values of the currents and voltages determinethe amplifor determiningthemutual conductance as shownin Fig, 1, the value ofthe amplification factor obtained by the arrangementof Fig. 2 will difier from the valuesfobtained fication factor and not the fixed direct-min" rent values used inthedirect current devicesr termination made as a result of such average value efiects fulfills all therequirements that ,azm'easurementoffthe amplification factor is the meter will be opposite, to those indicated plied to the requircdto give to, one concerned with :the practical operation ofthetube. I g As in the arrangement of Fig; 1, the polar ity of the transformerwinding 20 and ofthe rectifier 21 must be so chosen; that the recti;

fi ed current 'impulsesqare produced in the auxiliary circuitincluding the resistance26 and 27 during the. half cycles when the plate i the tube may be determined under, utilization of current derived from an: alternatingacurrent source. The'tube lhaving a cathode 2, and grid 3, is arranged for mounting in asocket having socket terminals5,6 and7 In thisarrangement, the grid socket termi-J, nal =6 isdirectly connected to onei of the cathode socket terminals 5 of the instrument;

,As in the arrangements described before,

the tube circuits are energized from anti-ansiormer 10 having a primary' winding 11- con- Y nected to supply' line conductors 1-2 of-an alternating current :source, 1A secondary windinglt supplies the cathode {2; "The plated is connected through conductor 15 to one terminal of the supply line. :A transformer winding 20 supplies througha recti-f fier 21 an d switch 23, an auxiliary circuit includingfthe resistors 26 and 27. The plate circuit of the tube iscompleted by a conductor 16 leading from theother terminal of the source by way of a variable contact tap 29] through resistor27, conductor 17, meter 18, to the cathode 2. An additional resistor 28 is connectedin shuntto the resistor '26 and a the meter 18. In operating theinstrument;

the tube is inserted in; place asshown in the drawings, and the sliding contact tapr29 is adjusted on the resistor27 until closure, of

igs I Ween a a the switch 23 does not vary the deflection {Of the meter 18'. Theresistance of the part of the resistor 27; includedin the circuitlwill 1 then be; a measureof the plate impedance of;

the tube.

as follows: a

The plate of the I bytheequationlm However, for all practical purposes, the ide I wherein-1,; is the change'of theplate current produced upon closure, of switch 23,1and Ep is the change of thevplate potential-produced upon-closure of switch: 23;a Closure offthe switch 23 will also produce acurrentqfiow through the meter 18 given by equationwheresE astqua to theivtitag- (156p was the resistor- 26 and R is the resistance" of: the resistorh27. When the contact tap 29i-s ad; justedso thatthe twoc'urrentsI and I=bal ance each other, we have 3 re the resistance o f the ofresistor-27 included by the tap 29 the} cuitthrough'the plateet. a a

jthe plate imped Equation I As in thearrangement described in Fig; 2, the values obtainedycorrespond to theaver- As in the instanclespreferred to,

must beso poled as to conducticurrentduring where R theresistance of the resistor 26.

"I05 age values of the currents? and voltages applied to j the various circuit elements; The average results 3 so obtained are fully satis factory for all practical'purposes; 1 i

the half cycle when the plate'potentialisposF a tive. "'lhe transformer winding 20' and f rectifier :21' maybe used with the" polaritiesms' indicated in the drawings or (with? reverse polarities, in which case the. changes ofthe current producedare'opposite to those indicated in the drawings by thearrowsI andlgi In Fig; 4 there is shown-fa modificationof the arrangement of'Fig. 1*for determining' the mutual conductance'of the tube; {In this i t i arrangement the" cathode and'plate'electrodes' i are connected to the. transformer '10 "like in 1 the device of F 2 1."; Thetransformer'wind's ing' 20 is connected through a rectifier 21+ and switches to two'seriau'y connected-resistors 26 and 27 ,The mid-point between these two a resistorsis connected to one of-"thez cathode i 1305f supply fleadsfwhich lead is also? connected through the resistor 28 to one ofthe supply line terminals. The meter 18 is connected through a conductor'17 between the line terminal of the resistor 28 and the variable contact tap 29 slidably engaging theresistor 27.

Asin the arrangement of Fig. 1, the mutual conductance of the tube is determined'by inserting the tube in place and then shifting the slidable contact 29 along the resistor 27 until closure of the switch 23 does not affect the deflection ofthemeter 18.1 The amount of the resistance of the resistor 27 is then a measure of'the mutual conductance of the tube. The theory'underlying this arrangement is as follows: I

The mutual conductance of the tube given by the equation s;

wherein E; is the grid potential applied to the grid, in this case by closure of the switch 23, and I the plate current'flow produced by the changev of thegrid potential E Substituting for E and I we have,

' E,='IR1, (18) being the voltage drop produced by the current flowing through the resistance R of resister 26 upon closure of the switch 23.

IWhen .the current flow in the meter 18 has been balanced,-the voltage drop across the resistanceRof the section of the resistor 27 included in the circuit by-the contact tap, 29,

I i as theformula for the mutual conductance by the arrangement of Fig. 4. Evy-providing a suitably calibrated scale, the mutual conduct'ance can be directly read ofi from the adjustment of the tap29 along the resistance a. The arrangement (if Fig. i has 7 the a.

vantage over'the arrangement of Fig. 1 in that the resistance term R, the magnitude of which determines the'mutual conductance of the tube is in the numerator'of the formula, so, that'the scale 30 will be uniform, and a more accurate determination of the mutual conductance willbe obtained. In the formula for the arrangement-of Fig. 1, R is in the denominator and the scale 30 will be non uniform. 'For most practical purposes either-arrangement 1 or arrangement 4-.Will be found useful. Y

' As in the instances described before, the arrangement of Fig. 4 may be used with the, polarity of the transformer winding 20 and the rectifier-21 eitheras shown in'the drawings so as to applya positive potential to thegrid 3 upon closureof the switch 23, or with reverse polarities soas to apply a negative potentialto the grid 3 upon closure ofswitch 23. "It is of courseunde'rstood that in this arrangement, the value of the mutual conductance is somewhat different from the values obtained with direct current measuring methods since the results are based onthe average of the currents andvoltages applied to the various elements of the arrangement.

The arrangement of Fig. 5 illustrates another modificationfor determining the -mutual conductance of the tube under utilizae tion of current from a commercial alternatiing current source,'this arrangement being combined-with provisions for also determining the amplification factor of the tube. The device comprises socket terminals for receiving the tube 1, and a' transformer 10 arranged to supply the cathode and the'plate of the tube as in the arrangement of Fig.1. A transformer winding 20 is connected through a rectifier 21 and switch 23 to two serially connected resistors 26 and 27 and suppliesthe same with rectified current pulses duringthe periods when; the plate is at a positive potential. The meter 18, havingv shunted thereacross-a'mete-r shunt 19, is connect-ed between the midpoint of thetwo resisto1s'26 and 27 andone of the cathode supply-leads.

31,32, is so arranged that in the upper position asshownin the drawings, one pole of the alternating current supply line '12 is connected to the midpoint of the resistors 26 and 27, and a resistor 28 is eonnectedbetween the cathode supply lead and a variable contact tap 29 engaging-resistor 27. When the double-p'ole switch is. thrown to the downward position, the circuit of the resistor 28 is A double-pole switch having switch poles I 1 opened and/the lead 16 from the supply line 7 conductor 12 is connected through switch pole 31 to the variable contact tap 29 When the double-pole switch 31, 32 isin the upper position as shown in the drawings, the arrangement of Fig. 5 will'operate as a direct vreading.instrument for the determination of themutual conductance of the tube 1. To operate the device, the tube 1 is inserted in place,whereupon the meter 18 will show a deflection corresponding to the plate current flowing in the circuit. The slidable contact tap 29 isthereupon adjust-ed along the resistor 27 until closure of the switch 23 '1 will leave the normal deflectionof the instru'- ment unaflected. When this has been brought about,the resistance R of the part ofthe resistor 27-v included by the tap contact 29, will give a direct measure of the new tual conductance of the; tube and. this mu.- tual conductance can be directly read oifpthe instrument t 5 The theory underlying the operation of this arrangement for the determinationflof the mutual conductance of the'tube isas follows:

Starting'from the equation'for the mutual conductance ofthetube v X ,'=IRJ c a this being "the voltage 'drop across the resistance "R of the resistor 26 produced by the rectified current I flowing from the 20 transformer-WindingfZO- upon closure ofithe which as in the prior cases is the average value. I H t Whenthe instrument s used im easuring the amplification factor with the doublepole switch 31', 32 inthedownward posit1on,'

35 circuits are established" which fare'in'every respect like the circuits of the arrangement in Fig. 2 so that the amplification factor is" given by the formula a It wiube noted that in the arrangement of {Fig 5, a conductor 35 is tapped off from'the primary transformer windingll, leading to a contactterminal 36. This arrangement may be used in connection with testing of screengrid tubes, the terminal 36 serving to supply voltage source for the second grid of the tube. Itwill be notedthat the arrangement is such that when the positive potential is ap plied by supply leads12 to; plate 4. through the socket terminal 7leadingto plate 4 0f the tube, a lower but likewise positive potential will be. applied by the transformer winding 11 to the gridterminal 36 of the instru menu. v v

With (the present commercial 'typesof 1 screen-griditubes, .the sockets are provided with four prongs arranged elxactly'like the prongs on the sockets for ordinaryithree-elem trode tubes. 'In-screen-grid tu bes,-.the grid p greatly 'diifer depending ion' Whether gilo platecurrent tube; orfai highlipiate'curre ltf p tubeuistested Let us assumeithat the.cl1ange y prong on the base is h'ovveve'rin'ot connected to the control grid of the tube as'in ordinary from a suita-bly calibrated scale 1 3 socket 6 and the controlgrid :terminal of the tubewhichusually projects ou the top switch 23. Under conditions. of current bal} as the formula for the mutual conductance,

' Because ofuthesefconditions, the accuracy grid of the tub'eiwill bec'onnected tothegrid of the bulbwill be free for connection 'to-the auxiliary grid supply terminal 36. When'af screen-grid tube 1-is-1so tested, namely" withlits I screen-grid connected to the conducto ifl and thecont-rol grid connected to; the termi'nal36,

G g, p "itaoperat'es under lsomewhat-differenticondi- I p p 1 tions than'those u-nder which'the tube isynorw Wejmay substitute; 'Inally intended to-opera'te. Howevensuch test mayundcrcertain circumstances besuflithe instrument for nsec inmconne'ction with screen-grid tubes and so i arranged that the '65 p termmals of the screen-grid tube archccn f nected into operative circultsin the samejrelaQ tionshipas theyare commonly used, i. e. with the screcn-gridconnectedjto an auxiliary;

source or potential. that'is less positive than 539 the plate po'tential, and' the; controlngridis wconnected toa source oficontrol voltage,

m One of tliedifiicultiesthathas:to xbe con tendedfwithin thewonstruc'ticnof: aapr'actia" cal; tube testing "instrument that "could be 15 freadily placed in the hands ofwdealersand otherlaymenyis; the factthat there-are]on-= the market" a greatqvariety of tu bes'fand the pl ate current of sucliitubesbvariesover a ide i range. .For'instance; a typerofaltube: knownw w' ,as -171A:Will dravv under nor'ir'ial' plate ivolt- *ageaplatecurrent ofabout 25 rhilliamperes e I a 'while another typicaltube knownas A -5226 v I Ywill'undersimilarconditions dravvronlygabout I w,

" '5'milliamperes." Such Widely;difierentgplateW05.

{currents makeit ordinarily-"necessary to'use I instrumentsjhaving 7 several ranges," for in'- lstanceyo'ne range to itake 'ca're ofhigh plate 7 current tubes, andianother for" loW' i ment- 5 A 1'1o most cases, the mutual conductance of i", y bothwhi'ghendlow plate currenttubeshis of f rent t tubes.

the "same order of magnitude; despitethc fact that'their plate currents"differ substantially; from each other. a This meansithatthe change in plate current produced by; a given grid for different ranges in atypical case"are ,say"- v020 inill-iamperes' for'ithe low plate current lrange andfO l00l niilliamperes;forthe high I plate currentirange; .These ranges, Will'tak'e careiof most-of the tubesiencounteredin'practice. IT-

ofthe readings ,or; the measurements will" "in the plate current for two tubes, one a low plate current tube and another a highplate current tube, will in both" tubes be 4 milli- 'amperes for a givenchange .in grid voltage. The change of 4 milliamperes is readily and accurately observed on the 20 milliampere scale since the deflection of 4 milliamperes amounts to twenty percent of the'full scale deflection. However, on the 100 milliamp ere scale, the change 0f4 milliam eres is only four per cent of the full scale de ection. 'Such' a small deflection is very diflicult to observe 1 with any degree of accuracy and accordingly, the design of an instrument that would have plate current rate as well as high plate 0111".

equal accuracy for testing tubes with a low "1'( 311t| rate, is a matter of great practical concern.

One feature of my invention involvesa very simple arrangement whereby these difficulties are avoided and substantially the same accuracy is obtained in determining the mutual conductance of high plate current tubes as in low plate current tubes. An exempli-fication of such arrangementis shown in Fig. 60f the drawings.

As will be seenfrom a comparison with the arrangement of Fig. 1', that of Fig.6 has an additional-auxiliary circuit between the con ductor 17 and the conductor 22, the auxiliary circuit including resistors 41, 42 and 43 and switches44, 45, and 46', by means of which more or less of said'resistors' may be included in an auxiliary circuit-from the transformer winding 20 and. rectifier 21 to the meter 18 includedin the'circuit of conductor 17. g The function of this arrangement will be best understood by considering the case where the, instrument has, say, a full scale deflection of 10-milliamperes and a tube havinga normal current of25 milliamperes is inserted into the socket terminals 5,6, 7, fortesting- Undersuch conditions, with the switches 44,

' 5 and 46 open, the plate current flowing through the meter 18 willthrow, the pointer past the full scale indication of'1O milliamperes.- Now, by closing, say switch. 46, an

1 auxiliary circuit is established from the trans- 5 former winding 20 through the resistors 41,

42,43 and the meter 18, sending a current in a direction'opposite' to the plate current. This current flowthrough the resistors 41 to 43 I term the bucking current? as it amount of resistance of the resistors'41, 42,

43 included in the bucking circuit is such bucks the plate current in the meter 18 and reduces the deflection of the meter by an amount'corresp'onding to the bucking cur,- rent. For instance, if the I current flow through'the meter is 25 milliamperes andthe as to produce a bucking current of 2O milli- .amperes, the deflection of the meter will correspond to an indication of 5 milliam'peres. After the deflection of the meter has thus been brought withinits normal range by cloadjusting the contact tap, 29 until closure which may be encountered in testing the usua-l run of tubes, the resistors 41 to43-n1cluded I in the bucking circuits are arranged for connection in steps, which vary the current through the meter circuits in multiples of the full. scale deflection. Thus, if the meter full scaleis l0 milliamperes', the resistors41, 1 42 and 43 are-so chosen astoproduce bucking currents in steps of 10 milliamperes, 20 milliamperes,30 111illiamperes,etc. This will take care of any platecu'rrents' within therange 0f 10 to 20 milliamperes, 20 to 30 milliamperes,

and 30 to 40' milliamperes, respectively.

Tubes having plate 'currents.,:within the range of O to 10 millia-mperes will fallwithin the scale of the meter without necessitating the use of bucking currents. I p

The arrangement of Fig. 6 1s characterized by the advantageous feature that the same. combination of transformer;winding 20 and rectifier21 which cooperates inthe determination of the IHUtUal CQHdUCtaDCG of the tube that is to be tested, also-serves as the source of the bucking currents through the circuits of the testing instrument. v In order to function properlyfin the way described flow through thebucking circuits shall be in a direction opposite to the flow of the plate.

current through the meter 18.

of the switch 23 shall be opposed to the change of the plate current produced by the closure There must also befulfilled the condition,

above, the transformer winding 20'and the rectifier 21 must be so poled that the currentthat. the-current flow. in the circuits of the. resistor 26 and meter 18 produced byclosure of switch 23. These combinedrequirements are fulfilled by polingthe transformer wind ing 20 and the rectifier 21:50 that during the I conductive halfcyc'le when "the plate is positive, apositive potential is-applied to the grid 3 when the switch 23 ;is closed. It is thus seen that in the arrangement of Fig; 6, which. 7 provides the meansfor sending bucking currents through the meter to secure. greater accuracy over ajwider range of plate. currents, there is not the same freedom n the olin of the transformer windin 2O3and rectifier 21 as inthe instances dealt with in connection with Figsxl to 5.

To secure proper functioning of the testing arrangement of Fig. 6, I also provide a ballast resistor 48 in shunt to the-serially connected transformer winding 20-and rectiiier 21. Without such ballastresiStO- j errors would 1 "mi-me l introduced inthe mutual conductance read '7 ings on-the scale 30 of the? instrument Tdu'e pending upon the magnitude "ef the internal impedance ofrth e transformer 10 and rectifier 21.

rent which in Combination with the-plate'eun I rent produces a certain deflection ofthenieteif 18." When theswitch 231is thlilllQlQSdfiH-Ildf an additional "lea-d "thrown (in {the tra i ls forn e r rectifier source, prdducing a reductii'e'n' Of the ter'm'inaljoltage acrossthe source, this, Will" immediately afi'ect the flour efthe bucking current so thatlit will beii'mpossible" t6;

get a goodand accurate reading; astl leread second; by the use of the "ballast"; resistonzre ferr'e'd to above; Q1 I 'ha've'fdund that the copper xide i'ect ,goodiaccura'cy, the use of the ballast resistor i 48' is "very desirableq The \jralueofthe re rgistanee of the, ballast resistor 48 should be s0 preportioned that 'current changes in the-f rest ofthe circuits produced by the closure of tlievaridus switches 23, 44, l5'and l6, and 1 the "adjustment of centactft'ap 29 shall be only asmaIl percentage of the total current 1 "drawn by the-ballast resistor 48;',-Ihaw:

found that in V the construction "of 1 practical instruments .fdr Ordinary us very 'geod ref; sults are: ebtainedif the resistance .eftheflresis'tor 4:8 is made about one-tenth'fejr less ef the resistance of theremainder' ofthe lead? "connected across the transformer rectifi'ei U i mounting in a' seckethaving'cathodelterm nals 55, grid terminal '56 and plate'gterminal 7 Th u j hejt in i c it are.

e V suppliedlby ja transflmefBO'ha inga' prj For the proper functioning ofsuchtube testi 'ers itis important that the voltages'laipplied combination.

- "Thearrangementef Fig. is a sailupfuitp illustrate another phase of inyinventionfree ferred to laterinconnetion With Fig Z';

to the various elements ofv 'thecircuitshall'be ofcertain definite values; as otherwise the I zineasur'ed Values of mutual cenductanceyama lification, etc. are diflicldttenorrelate and This {may he understodd {from the fol-Q lowing censideratiens. \Vhen the ibucking circuit is cl0sed, the' meter-1'8 carries a cur prelimi'naryg to the testing eperatien ,s'O that fiers which are sold in thetradeyunder th'fi' trade name Reetex perform Ivery satis 'factorily and have anin ternalidropsufficienta ly low so as to operate preperly'irithem: rangement; of my invention, "However; for

testing of the 'tubfe, a current: 'flp'wfwilh be iacteri zed by a number-bf additienal features 7 which extendfits futility and siln 'pliiy the r i m ual-Co ductance of the tube J ay alsohe used fer'determining"the yoltagefi; yappliedftd thetubeelements To this} end utilize jan auxiliaiy circuit leading from t e, r transfermeri winding" '20 andfrectifier 2lgby j wayefthe' meter'18including inthe circuit "suffi-cient'resistanee so-that them'e'ter operates" 7 as a}voltmeter. "Under sucheenditiens,;the, resistance in the circuit may be so chosen that a j l the deflectien 0f the n1eter 1 8gives-direct indication' 6f the voltage of the transformer L WindingL20.f v V, n Y 5 .Si ce the transformer 10 is-as a rule of the ype h ifigfg e v l ge gu a i he i dicatien'oi'the-voltage offvene of'the windings" will constitute a go ed 'check of the veltagesi in-thegother windingssethatbysuitable calii bratien, the meter 18jmay'be used; as'a geed indieatieir.ofthe Voltage applied to thepri: mary transformer winding 'll'and to 'the ea'th .ode: Byincludinga suitable regulatingdevice lin the supply "circuitef the transformer ".i j r A a and utilizing such auXiliaryTmeter 'cir cuit, f ing ef the instrument will then"beg-affected not only by the change in the resistance Ref the resistor 1 26 included in the cii cui t, but

' alsoby the internal drop in the supply-source?" rectifiercombination This diificulty isover-fl come by :my arrangement;firstihy u ing-a rectifier having lo'winternal impedance and} r I v switch between the cenduct er 22 leading v t ff o t i c ifi 21L 'a 'the eoi d b r :17 Y leadingw the me e zdisiy-eio in h s-meter,

theve'ltage efthe instrumenfimay be adjusted each tube tsted at theQjropez petent'ialjj The circuit arrangement usedinf;s uch'case is similar tothat shoWn'inFiglfi, for instance,"v

arranged to-be cojnnected'bya switch'such as ci c t slwit msu h w ch-Minde t th r produced tli reugh the meter" and the meteri f- I suitably "calibratedetheiyeltage regulating device included ing-thesupply' circuit maybe .adjustedso" as 'terhavefacross' supply te'i minals efthe tran'sfermerjill), a voltage ofthe 7 cerrec't'value fer testingthe tubesifg The-tube V i y scribedbefore,j I V:

" In Fig. IhaVeshoWnmylinyentio the: formintvhichl embedieditin eialaILarOund'JtIIbe.testingdeviceg,This'ary rangement'o f Fig;7.ffOl l0Ws the'prin'ciple of ,Q:

the arrangementtshown in Fig.1, but isjchar ener'ation" of the testerQ V l h n 't e raw ngs, iti l ithei cathode 2,;grid 3 andanOdeA is arrangedffer p ary in ng; th i ii pl di o igh ing "66 of the transformer whiqhfi's provided midget. rhaabrigana withfmy i aaabai, y the sameiinstrumentl8 whiehj is used for deef l then be i hir ula way as de;

withia tap switch 67 so as topermit applica tion' of dilferent voltages to the cathode of (I the tube, depending on the typeof tube tested.

In the practical tester built by. me,:I have provided on the tap switchfive tap contacts so as to permit energization of the cathode with.

' voltages-of either 1.5, 2.5, 3.3,, 5.0 or'7.5 Volts corresponding to the rated cathode voltages of the current tubes.

The voltage applied tothe plate is tapped.

' 6a from'the windingfil by means of atap69. 'The plate circuitincludes a current-limiting r be easily regulated;

resistor so as topreventa dead shortcircuit in the plate circuit in case the tube-is'defe tive. A cut-out switch may beconnectedin.

of the transformer. may

As; in the arrangement of F the'plate circuit is completed by a connection from the othericurrent supply lead 62 through conduc- V tor 7 resistor 72, conductor. 73, meter 74,

switch75',v switch. contact 76 .tolthe lead 7 leading to one of the cathode terminals of the device. V'Ares istor. 78 constitutes a shunt for the meter1'7t'and is connected between the 7 conductor 73 and the switch contact 76. T The switch 7. 5 has in addition to its frontcontact f7 6 also a back contact 79 sothat the meter 7 4 'may be. connected inshuntto resistor 72 in. which case theresistor 2 serves as a shunt for'the meter. Thepurpose of this arrangement: will be explained. later.

a An'auXihary circult 1s establishedffrom' the transformer winding 8lthrou'ghrecti 7 her 82, conductor 83,s witch 84, resistor 86,

I serves as a ballast resistor, like the resistor; 48 in the arrangement of Fig. 6. a A scale 89 resistor 87 adjustable contact tap. 88 andthence through-the meter 74, switch 75,. f 5

switchcontacty76, back tojthe transformer winding 81, AL resistor 90 connected across the transformer winding 81 and rectifier 82 is arrangedsoasto permit reading of'the mutual conductance from the adjustment of l the contact tap 88 along the resistor 87.

-An auxiliary circuit is established-by eon-I V I nectingbetweenthe meter 7 4 and the'conduc- I sist'ors 91, 92, one ofthese resistorsbein'g artor 83 leading lfromthe rectifie'ra pair ofrerangedto becut out by a switch 93.

The foregoing tester arrangement embodiesiniitself most of the features ofimportancein the.operationjofftubetesters which have been described- Jindividua1ly in; connection with .the various. arrangements dealt with hereinbefore; particular tea: ture of; this arrangement isthe fact. that the meter'174 automatically acts as 'an insrument for measuring .thevoltage applied tothe transformer and therefrom to the tubeeir 7 cuits, V under elimination offany special switches or switch processes. In thepractical arrangement. built a by me in accordance with Fig. 7 the various circuitelements had I the following values:

The primary wi ding 6l and the sistor 64 were so adjusted that on application .ofavoltage of aboutl lO volts tothe contact 'tap 64, the voltage across, the ends of the transformer windingwasxl35 volts,- and the. inner end of the resistor 68 was connectedto' V a tap on the transformer winding 61 having sofldesigned as. to give a voltage of 8 volts: Ballast resistor 90 had. a resistance of 25 ohms, The fixed resistance 86 had 500 ohms and the variable resistance-'87, 5,000 ohms.

Besistances 91 and-92 had each 125 ohms.

Theresistor ,78 constituted a ten-milliampere shunt forthemeter 4 and the resistor 72 constituted a ,100-milliampere shunt V for the meter 7& when-the switch-7 5 :was

down. The platecurrent, limiting resistor 70 had a resistanceof 1,000 ohms. The regulatingresistor 63-wasmade ohms.

iis understood offcourse that I am giving-these: i

values not with a viewto limiting my inven- Y tion,;but"ra ther to enablethose who areinot skilled in the artto readily build a practical tube tester in accordance with thetprinciples of my invention. I

1 The meter 74L isconnected inthecirc'uit, I

not'in theregularway, but with'reverse p0;

larityl What would be the, regular poling of the, meter is shown in Figs. to 5, Wherethe?' )jand signs on the sides ofthe meter indicate its poling inithe'circuit, "Int-he ar rangement' of Figs. 1 1' to 6, the meter-fie so connectedthat when the plate circuitjflo'ws' throughthe .meter it produces. a; defleetion from the Zero position to a point correspondmg to the indication of the current flow from J the plate to." the cathode. In distinction" therefrom, the arrangementof 7 .isfsuch k that when the tube liscOnnectedinfthe circuit,' the plate current wil l tend to move the pointervout of the scal'epast thetzeropointthereof; or in. other words, the meter is con WVhen the tube 1 is to beteste d, I ment is first chccked 'up as to, whether it has I appliedltoits circuits-the correct operating The rea- 12o nected with reverse polarity against-the nor- I mal direction "of the plate'curren-t. I

son for; this arrangement will be. clearfrom the following desoription'of the operation of? 1 the instrument.----

voltages. This-isobtained'by direct reading on the scaleofthe instrument 74', the resistors,

91 and 92 being so chosen and the meter 74 produced from the transformerwinding 81'- by way of the rectifier 82, resistors-9 1, 92 and the meter 74 as, to deflect thepointer to,.a

predetermined position which may bespecial 1y markedin the instrument either in red orf h r switch 84 leaves :the instrument reading unby the designation .normal i -Fig.: 7, I- have so adjusted thecircuit constantsthat under normal voltage. conditions,

the lOimillia'mpere point on thesca-le'. 'Ifj'the meter points to a different place on the scale,

the tap contact 64is adjusted until the pointer now inserted in the socket terminals 55 to 57 This will "cause arflowi, of current from the plate 4 to the cathode 2 of the tube and thence flection of the pointerby an amount corresponding to the platecurrent. For instance,

if the plate current is 4 -milliamperes,".the pointer ofthe meter 74Wwil1 return from the pointlO on the scaleltotheepoint'donlthe scale; .Thereupon thecontact tap 88'isad-g justed along the resistor 87 until the P01111113 reached whenclosure'of the switch 84 does 7 instance referred to. above willstay atthe' point .6 on the scale with the switch'184 f closed as well as open. '1 In'this respect-{the testing operation is exactly-like thatgfollowed with the arrangement of Fi'g. 1 the scale 89 on the i-nstrument'permitting direct determination of the mutual conductance of, i

the tube, depending on the adjustment of the 4' contacttap-BS on the resistor 87. 1 I

In the instance discussed ab0ve,it hasbeen assumed that the meter 74 has a full scale deflection of -10 "mil-liamperes. If a tube is tested that has aplatecurrent of-more than,

1O millia'mp'eres; say mil'liamperes; then the; insertion of the tube in thesock-et'termt. nals of the-instrument'will throwthe pointer of the meter 74'past its zeroposi'tion onthe} In order to bring the pointer back on the scale of the instrument, I producea flow of bucking current by sending an additional scale.

10 milliamperes through the :meter; 7 4 in the of current" of 10 milliainperest when the switch 93 is open.

In the practical arrangement aceordingto' is brought to the predetermined pointon the scale, say 10 in the instance now underjconsidera-tion. @The tube that is to bei'tested 1s three-electrode tube 1. 1-

not; afiect the deflectionzoltthe instrument one way or another, i." e-.,' the pointeryincthe I: also provide' onfthe instrument an addi tional socket 126 "fortesting 'indircc'tlyheated screen-grid tubes "120 having' 'an indirectly; heated cathode -l21 a filamentary heater 1-22,

It seen" fromthe toregoing that all that i it is necessary to doin order jtoztest a tube by resistancetap'M until the meter 74 shows" full deflection; the tu e; is then inserte'd g -ifltlleh pointer is within the rangeof thev meter 74,

they mutual conductanceiis determined byslid the arrangement of Fig. 7is first toadj list the ing the'contact 88 until the closure of the affected; if thepointeifiofthe meter hasbeen thrown out "of "the scale by the insertion of tube '1, switch '93is closed, whichjbringsthe pointerback within the scale andv thereupon the tap 88 is adjustedfuntil the closure "ofthe "b L r switch. 8l leaves thepo inter unatfeeted. i

In 'order to i permit testing-1 of tubes using indirectlyheatedcathodeslsuch' as tube 1 hav .ing an indirectlyheatedcathode102 that is heated by heater filameiit103,.a'nd ina'ddi as tion, fro1n'the gridl04 and plate 105, I videdfon the instrument an vadditional}s(' cket f 106 having socket terminals,adaptedtoen gage the :electrodefprongs leading-from the a various electrodes of the tube. VA socket ter by way ofthe meter74 in the direction ofthe arrow marked I reducing the full scale -de- I minali'arrangedhi engage the prong on"the indirectly heated cathode 102 is connected;

ina'y be proceeded within exactlythe; same manner as with 'th'eite'sting of an" ordi nary Order t9 p il rady andcorrecttest i I 7 ing of screen-grid tubes such as tube 110'hajving a'oathodellh'control grid I12 and.- screen grid 1-13,-and an anode 114 1 provide an'jadditi onal set of socket terminals 115 ofwv'hich the terminals leading to the cathode prongsofthe tube are iconnected in parallel toj'the socket '1 terminals 55 01? the tube '1, an d the socket ter minal'ileading tothe plateil lO isi'connected in parallelto the pl'atesocket terminal The socket terminal adapted to' engage the prong leading from thes'creen grid l13 isconnected ;to a special winding- 119 onjthe transformer 60, the other terminal'of which is connected;

to the cathode supply conductor 770i theiar 'rangement. The winding 11;) is-so-d'es'igned I" and'pol'edi that; when theplate cf thetube has i; 1

applied'toitself a positive potential the trans? former. winding 119:;willsupply the-socket terminals connected to'it withafpositivepotential of vabout 50 @volts, it being of' coui-se possible to vary this voltageinaccordance applied to the control I grid 1 112 of the tub? J.

gridEsupply-terminal -1 1'Z:is 'connecte allel with the control gridsocikette oftube with the 'requiirernentsuThe grid volt'agej' V 1 a control grid 123,3 screen grid 124 and a plate 125," The'socket terminals 126 for this tube are connected similarly to the socket terminal on the screen-grid tube 110, their being onlyan additional socket terminal for engaging. the cathode prong of the tube, this socket terminal being connected-in parallel with one of the heater terminals.

The arrangement of Fig. for utilization as a tester for hot cathode rectifiertubes such as are used in modern.

- radio sets;v In rectifier tubes it is only important tod'etermine the filament emission or the plate'current. Such tube is tested by inserting the'tube with its prongs in the socket terminals :55 and .57, their beingno grid in such tube. Thereupon, the switch 75 adjacent u the meter range 100 milliamperes, since the to the meter 7 4 is thrown to the downward position into engagementwith the contact 79.

This reverses the direction of" connection of the meter 74: in the circuit'from the plate and the cathode of the rectifier tube, the current flowing now from the cathode prong by way of the conductor 77, contact 76,.condu0- g tor 78, conductor 7 3, meter 7 ahswitch 7 5, conductor 9 toconductor 71 of the plate supply 1 source. With these connections theresistor 72 "serves as a shunt for the meter. As ex-. plained above, in the instance here described, the resistance 72 is so dimensioned as to make plate current in the regulation run of recti liers used in modern sets runs up to about 100 milliamperes.

As, seen from the foregoing, one of the principal featuresof the arrangements of the determining'the mutual conductance, recti lied alternating currents derlved from the 45' invention is based upon the idea of balancing the auxiliary rect fied alternating current dee rived from an alternating current source with the changes in theplate currents of grid c ntrolled tubes that are supplied from such source. In the preferred arrangements for source are sent through auxiliary circuits from which a voltage is applied tothe control grid of the tube and: the changes inlthe pl ate currents produced by the voltageapplied to the grid are correlated or balanced against changes of current in..an auxiliaryconduct ance included inthe circuit of the auxiliary rectified alternating current flow.

' In add1t1on,'I have shown and described a great manyjother features which are of importance in the construction and operation of practical tube testers. "Many of the fea tunes described in'this application are not limitedtotube testing and tube testers, but

' have application in other arrangements, such Gu as relay, devices and the like. r

. Many modifications of myinvention will suggest themselves to those skilled in th'eart and I 'desire'that the appended olaimsvbe' given a broad construction commensurate "w th the scope ofthe 1nvent1on';

7 is also adapted during the period When the plate potential is positive, utilizing the auxiliary current flow'to apply a control potential to the grid or the tube, and utilizing the cornbinedef-V fects of the auxiliary rectifiedcurrentandf tified alternating current from saidsource the plate current change effected by theap- V plication ofsaid control potential to said grid to indicate the characteristics of'said tubes. I

2. The method ofltesting gridcontrolled space-discharge tubes which comprises applying a-source of alternating current to the platecircuit of thetube for sending current pulses from the plate to the cathode thereof, applying to an vauxiliary conductance and rid of the tube voltages'derived from'a rectified alternating current flowing from said source independently from the flow of current throughv said tube,"and balancingpthe resulting current through said auxiliary conductance against the current changes produced by the applied grid voltages in the plate current o-f'the tube to produce an indication of thecharacteristics ofsaid tube.- 3.'The method of testing grid controlled" space-discharge tubes which comprises energizing the plate circuitand the, cathode of the tube *from' an alternating current source, producing "an auxiliary flow of recti-i field alternating current from said source. 1

during the period when the plate potential is positive, utilizing-the auxiliary current flow to apply a potential to the grid of said vtube and to send a current-through an aux il'iar'y conduotance,adjusting thecircuit conditions until 'the current in the auxiliary con- 7 ductance is in predetermined relationship'to the plate current flow produced by the application ofthe potentiaLderived from'said auxiliary current flow to said grid, and actuating an instrumentjby the differential-ad" tion of said auxiliary current andthe plate currentflow produced by the auxiliary ourship of said currents 4. In a tester of space discharge tubes of' the type comprising a cathode, a grid and an: anode, terminals forengaging the oath:-

ode, grid and anode' terminals of the tube, a source of alternating current, connect1ons rent toindicate the predetermined relation from said source to the terminals leading; to"

said cathode for :heatingthe same, connections for applying the potential of said.

source to the terminals leading to said 'anode/ and tosaidcathode, means for producing, during the periodWhenth plate potential I is positive and passes a dischargelan' indeif]? pendent auxiliary flow of rectified alternat-.

ing current from saidj'source,;rnea11sior ap:

terminal I leading to thegrid {{Of; said "tube, an

auxiliary. conductance included in the circuitof said auxiliary rectified current ,fio'

means-for adjusting the circuit [conditions of said auxiliary current flow and said plate current fio v untilfthe cur'ren'tin' the auxilg tionship to the-current flow producedinthe 1 plate circuit of g said tube by the application of a control potential tofthe' terminal leading sa d g d, d-an in t ument r n e to be actuated by the differential 'actionof; said auxiliary current flow and'the plate current flow produced. thereby to, indicate I said relationship a an -anode,terminals for engaging the cathode,

grid and anode terminals ofthe tube,a source ofalternating current; con'nections frorn saidsource totl1eterminalsleading to said oathode for heating the "same, connections rom I plying thepOtential ofsaid source tofthef vterminalsleadingto 'saidanode and to said cathode," an auxiliarycircuit including an;

auxiliary iconductan'cq'means for producing an independent auxiliary flowof'd-irect cur-- rent through said auxiliarycircuit "during the period when the plate potential appliedto I said tube is' positive, and passes a discharge,-

1 saidauxiliary direct current-"flowtothe ter I minal leading to' 'the grid off said tube, means for adjusting'the circuit conditionsfin said 1 means for applying a potential derived from auxiliary currentfflow and saidiplate current i flow until the current in the auXiIiaLry cOn-E ductance is in predetermined relationship to the current flow produced in theplate circuit of said tube by the application of apotentialf from said fauxiliary circuit to said" grid," and an instrument actuated by the said auxiliary current flow and the plate current flow to indicate said relationship. J

space-discharge tubes I which comprises en e -j, 1 L gizing the plate circuit andthe cathodeofthe tube from an alternating current source, pro w r ducing an auxiliary flow" of direct; current: through an auxiliary circuit'independent of theplate current-through said tube during,

the period vvhen the plate potential is positive, utilizing the auxiliarycurrent jfiowto apply a potential to the-gridot said tubeand to send a current through an auxiliary con ductance, ad ustingr the circuit conditions I so:

until the currentin the auxiliary conductance is in predetermined relationship tothe plate current flow produced by the applicationv of I 'the potential derived from said auxiliary cur "rent flow to said grid, and actuating an jin+ 'strumentby the differential action or said;

nearcurrent I I I flo until thee rrent'dnjt'he-r'auxilia'ryicon' V ductancefisjin predetermine a r el'ationship' th -rrieneflq prbd dun m nag r-9 a ciiitfbfsaid tube bythe applicationo'facontrol potential ftg'the terminal leading fl said gridfai'rd an instrument-arranged to loeact'u} a ial'actio rof saidau x-r; 7 I liarycurrent'flovvia d the'plateleurrentfl wit "indicateg isaid'=,relatiOn '8} Ilie me'tlrBdhf; testinglscreeri 'gridcon trolled space 'dischar'ge j'tubes whmh reom I prises applying a'sourc eof alternating Ic'u r-t T51 rent'to the plate circuit ofsaidti1betolprb I 'duce aQflowjof current"frdmitheplate ftothe t 'c'athode'of the tube; producing an.aufxiliary i ,I flow of'rect ified altern'ating current'froin said our ries he i i d whe he Pla e P tentialis positive, utilizing the auxiliary cur-'1 rent flow :to apply *a control potential to the 1 grid ofthe tube, and utilizingl the combined I e'fiects jofthe auxiliary rectified'current and 6.- The meth d,- of testing grid controlled and b3 theatre-em r.ei1t s., y II I o 5-7. Ina tester of space dischargeitubesg of;

the typelc'omprisinga cathode, a grid ,andan i anode, terminals for: engaging the cathode, I 1 jgridand anode terminalsofthe'tubqasource fof alternating"current,"jconnections from said i I I M 7 source tothe terminals-leadingzto said cathiary conductance is in predetermined)rela ode for'heating' the same, connections for ap plying the potentialofzsaid'source to the ter- 1. i I .minals leading .1,to said anode aaiidaltdt said cathode; means forproducing duringthe' pe riod Whenthe plate potential is positive and produced th ship. 1

grid to ind'i'catejthel characteristics of saidF I tubesi vvhile;applying.to thescreen of said'f tube a potential atwhiohcu rrent fiowin'g'by'c pa 'sses-a-dischargeanfindependent auxiliary flow "of rectified alternating current: "from I saidsource, means for applying apotential' derived from said auxiliary rectifiedalter; nating. currentflow to the terminal leading to" the 1 grid of said-tube, an auxiliary conductance included in the circuit of said aux'-* i iliaryij reotified current flow, means" [for Iadv justin' g [the circuit E' 'Conditions; of said el xwand; d-r mi antv nc way-of said screen leaves the combined effects f ofthe auiriliaryrectified current and plate I 2 v TheQm'et-hod of testing screengridcon 1'. trolled space-discharge tubes .which comprises applyingla sourceofalternating'cur- I rent to theplate' circuit of the 'tube for sendr Zing current pulses from the plate to the cath ode thereof, applyingto an'auxiliarycon ductance and grid of the tube voltages/ dc rived from an auxiliary; rectified alternating [current flowing from'iisaid source independr ently from the flow of'currentthroug h said i tube, and balancing the resulting current f through said auxiliary conductance against ing by Way of said screen leaves the balance j in current the currentchangesproduced by the applied lgrid voltages in the plate current of the tube to-produce an-indication of the characteristics-of said tube, While applying to, the screen of said tube a potentialat which Current fiOW- effects of and plate current unalfect'ed.

1 10. atester of space dischargetubes of the auxiliary rectified .theitype comprising a cathode; a screen, a

control grid andan. anode, terminals for engaging. the cathode, screen grid and anode terminals of the tube, :a source -of alternating currentyconnections from said source to the :terminals leading'ftosaid jcatho'de tor heating the same, connections forv applylng the potential of said' source tothe ternnnals leading to said anode andto said cathode,"

means for producing during the' period when 1 the plate potential ispositive and passes a discharge an; independent auxiliary flow of rectified alternating current from said source,

A "means for applying a potential derived from I said auxiliary rectified, alternating current a .fioW to theIterm-inal leading tothegrid of said auxiliary conductance is in predetermined relationship --to the current flow produced in the plate'circuit of said tube -b'y-the application of a control"potentialE-Etqthe terminal leading to said grid, an instrument arranged a to be" actuated by the differential action of said auxiliary current flow and the plate current flow produced thereby to indicate; said Y relationship, and me'ans for ma ntalngin'g ther screeniof;saidtube at a potential at which current flowing by tsray of Said screen leaves the efi'ects' of'the auxiliary rectified. icur ent and plate current on said instrument 'unafiected. a V '11. The method-of testing screen grid con-v.

trolled space discharge tubes which comprises energizing tjhe plat-e circuit and the cathode of the tube from an alternating current source,

producing an auxiliary flow of rectified al- .ternati'ng current from sa d source-durlng'the period Whenthe'plate potential; i'spositive,

utilizing the auxiliary] current flow to apply,

a potential to the grid of said tube' and to senda current through an auxiliary conductance, adjusting the circuit conditions until thecurrent in the auxiliary conductance is in predetermined rel'ationship to the plate current-flow produced by the application of the potential derived from said auxiliary cur r rentf flow'to 'saidgrid, and actuating an instruInent-"bythe differential action of said auxiliary current and the platecurrent' flow produced bythe auxiliary current to indicate thef jrcdetermined relationship of said eurrents, While passing-1 an additional current from sald source through saldinstrument for controlling the'r'ange thereof independent of 5 the action'iof said "auxiliary andsaid plate current on said instrument;

in ;12. In a tester of space discharge tubes of the type comprising 'a'cathode, azgrid and an anode; 1 terminals for engaging the cathode, gr dand. anode terinlnals otthe tube, a source of alternating current, connections from said sourceto the terminals leading tosaid catli-l V ode for, heatin'gthe same, connections for ap: plying the potential of said source to the terminals leading to said anode and to said;

riod'wlien the plate potential is positive and passes a discharge an independent auxiliary flow of rectified alternating current from said source,,means for applying ap'otential-ole-v rived from said auxiliary rectified alternating 1 current flow to the terminal-leading 'to the a grid of said tube, an auxiliary conductance included in the c1rcu1t of said auxiliary'reccathode, means for producing during the pe v tified-current flow-; meansfor adjustingthe I clrcuitconditions ot'said auxiliary current" I fl0'W and said platev current flowi until: the

current in the. auxiliary conductance is in predetermined relationship to the current flow produced in the plate circuit ofsaid'tubeby' the application of acontrol potential to the .terminalleading to said grid; an instrument arranged to vbe actuated by the differential action of said auxiliary'current-flow and'the plate current'fiow produced-therebyjto indieate said relationship and means'for passing an additional current from saidsource through said instrument for controlling the range-thereof independent ofthe action of said auxiliary andsaid plate current on'said instrument.

nA In-EI'srAR sf- 7 

